1-Ethoxy-1-propene1

(1; R = Et)

[928-55-2]  · C5H10O  · 1-Ethoxy-1-propene  · (MW 86.15) (E)-(1)

[4696-26-8] (Z)-(1)

[4696-25-7] (E)-(2; R = Me)

[4188-69-6]  · C4H8O  · 1-Methoxy-1-propene  · (MW 72.12) (Z)-(2)

[4188-68-5]

(condensation with acetals to give a,b-unsaturated aldehydes;3 acyl anion equivalent;4 [4 + 2]5 and [2 + 2]6 cycloaddition reactions; transvinylation to prepare allyl vinyl ethers7)

Physical Data: (1) bp 69-71 °C; d 0.778 g cm-3. (E)-(1) bp 75 °C. (Z)-(1) bp 69 °C. (E)-(2) bp 48.5 °C. (Z)-(2) bp 45 °C.2

Solubility: sol most common organic solvents; slightly sol water.

Form Supplied in: colorless, extremely flammable liquids, obtained as a mixture of (E)/(Z) isomers by the pyrolysis of the corresponding acetals over pumice or NaHSO4.2b,c The (E)/(Z) isomers have been separated by fractional distillation2b,8 and by preparative-scale gas chromatography.6a Pure (>97%) (E) isomers of propenyl ethers have been prepared by H2-activated (1,5-Cyclooctadiene)bis(methyldiphenylphosphine)iridium(I) Hexafluorophosphate catalyzed isomerization of allyl alkyl ethers.9 1-Ethoxy- but not 1-methoxy-1-propene is available commercially. 1-Ethoxy-1-propene is a skin irritant, moderately toxic by skin absorption, ingestion, and inhalation.2c Biological data on 1-methoxy-1-propene are unavailable. Use in a fume hood.

Condensation with Acetals.

Lewis acid-catalyzed condensations of 1-ethoxy-1-propene (1) with acetals give, after hydrolysis of the intermediate alkoxy acetals, a,b-unsaturated aldehydes and ketones.3 Of the Lewis acids, Zinc Chloride and Boron Trifluoride Etherate are the most frequently used, although Montmorillonite K10 can offer certain advantages, such as ease of workup.10 In a study of the condensation of acetals with methyl vinyl ether in the presence of BF3.OEt2, the order of reactivity was found to be: acetals from a,b-unsaturated aldehydes > benzaldehyde acetals > methyl orthoformate > acetals from saturated aldehydes.11 The enol ether-acetal condensation is exemplified by a synthesis of the C19 carotenal (4) from the C16 acetal (3) using (1) in the presence of ZnCl2 (eq 1).12

Acyl Anion Equivalent.

Deprotonation of the a-H of (1) with t-Butyllithium at -74 °C, in THF or in n-pentane/TMEDA, generates the highly reactive a-alkoxy vinyl derivative (5) (eq 2), related lithio derivatives of which are known to react with a variety of electrophiles.4

Cycloaddition Reactions.

Thermal [4 + 2] Addition.

1-Ethoxy-1-propene participates in a variety of inverse-electron-demand Diels-Alder reactions to give cycloadducts with high endo selectivity and retention of the dienophile alkene geometry. The (E) isomer reacts faster than the (Z) isomer, and improved reaction conditions include the use of high pressure and Lewis acid catalysis.5 The cycloaddition of (1) to enals,5 enones,5 and a,b-unsaturated esters13 is regiospecific, giving dihydropyrans in excellent yields, often with very high stereospecificity (eq 3).14 Similarly, the thermal or pressure-promoted cycloaddition of (1) to N-sulfonyl-1-aza-1,3-butadienes produces tetrahydropyridines, generally in a highly stereospecific manner with predominant endo selectivity (eq 4).15 Cycloaddition of (1) yields dihydrooxazines from nitrosoalkenes16 or from azomethines,17 and chromanes from quinone methides.18

Thermal [2 + 2] Addition.

Electron-deficient alkenes react rapidly with (1) to give cyclobutane derivatives, with the (Z) isomer of (1) reacting faster than the corresponding (E) isomer. In general, stereoisomeric mixtures of products are obtained, which increase with solvent polarity (eq 5).6 Ketenes give cyclobutanones (eq 6),19,20 while p-tosyl isocyanate and p-tosyl isothiocyanate give N-tosyl azetidinone (eq 7)20 and N-tosyl-2-thietaneimine (eq 8),21 respectively, on cycloaddition with (1).

Photochemical Addition.

Photoaddition of vinyl ethers to a,b-enones produces alkoxycyclobutanes, and alkoxyoxetanes from aldehydes and ketones (see Ethyl Vinyl Ether).22 Although not with (1), extensive studies have been conducted on the cycloaddition of 1-methoxy-1-propene to acetone.23

Transvinylation.

In contrast to ethyl vinyl ether, (1) is rarely used in the transvinylation of alcohols. An example is the preparation of the aldehyde (7) in >51% yield by sequential transvinylation-Claisen rearrangement executed by heating an (E)/(Z) mixture of 1-ethoxy-1-propene with the allyl alcohol (6) in the presence of Mercury(II) Acetate (eq 9).7

Related Reagents.

1-Ethoxyvinyllithium; Ethyl Vinyl Ether; 2-Methoxy-1,3-butadiene; 1-Methoxyvinyllithium; Methylketene Dimethyl Acetal; Propionaldehyde t-Butylimine.


1. (a) FF 1967, 1, 385. (b) Effenberger, F. AG(E) 1969, 8, 295.
2. (a) Dictionary of Organic Compounds, 5th ed.; Buckingham, J.; Ed.; Chapman & Hall: New York, 1983; Suppl. 1, p 246. (b) Farina, M.; Peraldo, M.; Bressan, G. Chim. Ind. (Milan) 1960, 42, 967 (CA 1961, 55, 11 284b). (c) Gready, J. E.; Hatton, P. M.; Sternhall, S. JHC 1992, 29, 935. (d) Sax's Dangerous Properties of Industrial Materials, Lewis, R. J., Ed.; 8th ed.; Van Nostrand Rheinhold: New York, 1992; Vol. 3, p 1656.
3. (a) Isler, O.; Schudel, P. Adv. Org. Chem. Methods Results 1963, 4, 115. (b) Carotenoids; Isler, O., Ed.; Birkhauser: Basel, 1971. (c) Makin, S. M. PAC 1976, 47, 173.
4. (a) Knorr, R.; von Roman, T. AG(E) 1984, 23, 366. (b) Lever, O. W. T 1976, 32, 1943. (c) Boeckman, R. K.; Bruza, K. J. JOC 1979, 44, 4781. (d) Kraus, G. A.; Krolski, M. E. SC 1982, 521.
5. (a) Boger, D. L. COS 1991, 5, 451. (b) Carruthers, W. Cycloaddition Reactions in Organic Synthesis; Pergamon: New York, 1990. (c) Boger, D. L.; Weinreb, S. M. Hetero Diels-Alder Methodology in Organic Synthesis; Academic: San Diego, 1987. (d) Desimoni, G.; Tacconi, G. CR 1975, 75, 651.
6. (a) Huisgen, R.; Steiner, G. JACS 1973, 95, 5054, 5055. (b) Huisgen, R.; Bruckner, R. TL 1990, 31, 2553, 2557. (c) Fatiadi, A. J. S 1987, 749. (d) Baldwin, J. E. COS 1991, 5, 63.
7. Imanishi, T.; Yagi, N.; Hanaoka, M. TL 1981, 22, 667.
8. Wojciechowski, B. J.; Pearson, W. H.; Kuczkowski, R. L. JOC 1989, 54, 115.
9. Baudry, D.; Ephritikhine, M.; Felkin, H. CC 1978, 694. See also: Iranpoor, N.; Imanieh, H.; Forbes, E. J. SC 1989, 19, 2955.
10. Fishman, D.; Klug, J. T.; Shani, A. S 1981, 137.
11. von der Brüggen, U.; Lammers R.; Mayr, H. JOC 1988, 53, 2920.
12. Isler, O.; Lindlar, H.; Montavon, M.; Rüegg, R.; Zeller, P. HCA 1956, 39, 249.
13. (a) Hall, H. K.; Padias, A. B.; Way, T. F.; Bergami, B. JOC 1987, 52, 5528. (b) Padias, A. B.; Hedrick, S. T.; Hall, H. K. JOC 1983, 48, 3787.
14. Chapleur, Y.; Euvrard, M.-N. CC 1987, 884.
15. Boger, D. L.; Corbett, W. L.; Curran, T. T.; Kasper, A. M. JACS 1991, 113, 1713.
16. (a) Reissig, H.-U.; Hippeli, C.; Arnold, T. CB 1990, 123, 2403. (b) Gilchrist, T. L.; Iskander, G. M.; Yagoub, A. K. JCS(P1) 1985, 2769.
17. Hall, H. K.; Miniutti, D. L. TL 1984, 25, 943.
18. Arduini, A.; Pochini, A.; Ungaro, R.; Domiano, P. JCS(P1) 1986, 1391.
19. Fráter, G.; Müller, U.; Gunther, W. HCA 1986, 69, 1858.
20. Effenberger, F.; Fischer, P.; Prossel, G.; Kiefer, G. CB 1971, 104, 1987.
21. Schaumann, E.; Bäuch, H.-G.; Adiwidjaja, G. AG(E) 1981, 20, 613.
22. Synthetic Organic Photochemistry; Horspool, W. M., Ed.; Plenum: New York, 1984.
23. Turro, N. J.; Wriede, P. A. JACS 1970, 92, 320.

Percy S. Manchand

Hoffmann-La Roche, Nutley, NJ, USA



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